1. Field of the Invention
The present invention is generally directed to the field of liquid vaporizers, and, more particularly, to a liquid vaporizer with positive liquid shut-off.
2. Description of the Related Art
In a wafer fabrication process, a wafer is commonly subjected to process gases under pressure in the controlled environment of a process chamber. The deposition formation rate on the wafer and the etching removal rate from the wafer depend on the input gas flow rate of the process gases that enter the process chamber encapsulating the wafer.
A vapor deposition system for wafer fabrication generally includes a liquid delivery or injection system for vaporizing a liquid chemical and carrying the vaporized liquid into the deposition process or reaction chamber for wafer processing. A typical liquid delivery system for a chemical vapor deposition process manages the flow of a liquid precursor or reagent, a carrier gas, and one or more other process gases. The liquid precursor is delivered to a vaporization device at a steady flow rate. The carrier gas is delivered to the vaporization device for mixing with the vaporized liquid precursor. The other process gases are combined with the mixture of the vaporized liquid precursor and carrier gas for delivery to the process chamber.
A critical factor in the production of wafers with superior uniformity is the precise control of the flow rate of the delivery of the liquid precursor into the process chamber. Irregularities in the flow rate may cause non-uniformity and erroneous deposition film thickness that adversely affect wafer quality and acceptability. The liquid precursor flow rate is typically generated by a liquid mass flow controller that is governed electronically by a voltage signal, such as that produced in a liquid flow meter. The accuracy of the flow rate produced by the liquid mass flow controller depends on the calibration between the voltage signal and the actual flow rate delivered.
Many liquid vaporizers tend to trap various amounts of liquid after vaporization processes are stopped. Such trapped liquids must generally be flushed from the system prior to the next use of the liquid vaporizer to introduce liquids into a process chamber. Efforts have been made to reduce the volume of such trapped liquid. Such efforts include, among other things, physically reducing the size of spaces where such liquids may collect.
Liquid vaporizers sometimes use piezoelectric actuators to raise or lower a ball on a valve seat in an effort to stop the flow of a vaporized liquid through the vaporizer and to prevent leakage of liquids resident within the vaporizer after vaporization processes have stopped. However, such arrangements have proven to be unsatisfactory in that the liquid still manages to seep past this sealed surface, thereby resulting in the additional accumulation of fluid that must be flushed prior to using the vaporizer.
The present invention is directed to a method that may solve, or at least reduce, some or all of the aforementioned problems.